Urinary incontinence is one of the most prevalent conditions of the lower urinary tract, affecting approximately 40% of women in the United States. Stress urinary incontinence (herein abbreviated SUI) accounts for a large portion of these women. SUI is the loss of small amounts of urine associated with movements, such as coughing, sneezing, laughing, and exercise, that cause increased pressure on the bladder based on increased intra-abdominal pressure. In the US, over 160,000 surgical procedures are performed for SUI annually, and mid-urethral slings have become the most commonly performed procedure for SUI. Mid-urethral sling procedures are based on the studies of the female urethra by Petros and Ulmsten which showed that a deficient pubo-urethral ligament (herein abbreviated PUL), with attachments between the ventral surface of the urethra and the lower pubic bone (herein termed the pubis), may lead to urethral mobility and SUI or mixed urinary incontinence in women. These authors describe the role of the PUL within an “integral theory” of the pathophysiology of urinary incontinence.
In order to study the mechanisms of SUI in the female, investigators have recently developed and tested animal models in the female rat that mimic the symptoms of SUI. These investigators have used either the vaginal distension model, which causes injury to the tissues of the pelvic floor similar to birth trauma, or the model of direct injury to the pudendal or sciatic nerve, which induces manifestations of SUI. The symptoms and signs of SUI in these animal models have been assessed by in vivo measures such as leak-point pressure (herein also termed LPP), which is similar to the clinical measure of bladder outlet competency, as well as by quantitative morphometry measuring post-partum damage to the external sphincter and pudendal nerve. These models demonstrate tissue injury similar to that following birth trauma. Both the vaginal distension and the nerve injury models have been accepted as surrogates of post-partum SUI in women.
However, it is known that nulliparous women can also develop SUI. Consequently, it is believed by the present inventors that animal models of nulliparous SUI should focus on alternative anatomic targets for controlling continence during intra-abdominal stress. In 1961, Zacharin described the attachments of the PUL and the vaginal insertion of the anterior portion of the levator ani, and was the first to suggest the role of these structures in continence. In 1998, Petros analyzed the structure and insertions of the PUL in female patients during the intra-vaginal slingplasty procedure. Petros described the PUL as descending like a fan from the pubis and including a urethral part, a vaginal part, and thin fibrous threads connecting the two parts, which appears as a continuous sheet of connective tissue. Petros further described that the urethral and vaginal parts each generally vary between 5-7 mm in width and 3-4 mm in thickness, with the urethral part being about 2 cm long and inserting into the midpart of the urethra, and the vaginal part being about 3-4 cm long and inserting into the vaginal hammock posterolaterally, about 1 cm short of the bladder neck. The insertion of the urethral part into the midpart of the urethra (also termed urethral attachment), has been hypothesized to provide ventral tethering of the urethra during intra-abdominal strain, preventing urethral mobility and subsequent leak.
Based on the postulated role of PUL in SUI, recent surgical treatments for SUI based on the “integral theory” have led to the development of mid-urethral slings, pioneered by the transvaginal tape sling procedure. This procedure, introduced by Ulmsten and Petros, has enjoyed worldwide popularity with excellent long term efficacy. It is estimated that over one million sling procedures have been performed worldwide. However, the sling procedure is not without morbidity, and a more simplified procedure with the potential to reduce morbidity and pain for the patient would be desirable.